In the basic Internet protocol or TCP/IP (Transmission Control Protocol/Internet Protocol) information is sent over the Internet in packets. These packets may take different paths, through different lengths of physical network, and through different routers, so as to be subject to varying time delays. The simplest notions of timing include adding a timestamp at each appropriate transmit and receive location to carry time around the network. With relatively sophisticated protocols, the current time transfer limitation through data networks is of an accuracy on the order of 1 millisecond. The limitations are due to unpredictable variations in the amount of time packets spend in transmission and receive buffers. These buffers occur at the sending hardware, the receiving hardware and at routers in between.
A typical network time packet contains four timestamps. The timestamps are designed to precisely time the transmit and receive paths of the client/server time packet interchange and solve for the time offset in the Network Time Client. Any difference in time between the average of the paths represents the time offset from the true time between the client and the server. The problem with this time-honored technique is that it assumes that the transmit and receive paths take the same amount of time. However, when the Internet introduces real differences in the transmit and receive path lengths, due to packet collisions, repeaters, routing, bridging and line delays, then this error directly affects the fundamental accuracy of the time derived over the Internet. Sophisticated protocols such as Network Time Protocol (NTP) and Digital Time Synchronization Protocol (DTSS) overcome some of the network errors by using filtering algorithms and the like. See, for example, D. L. Mills, “Internet time snychronization: the Network Time Protocol.” IEEE Trans. Communications COM-39, 10 (October 1991), 1482–1493. However, when the variations in packet transit times reach a certain level, then no amount of filtering will eliminate errors for these protocols.